Next-to-leading order QCD predictions for W+W+jj production at the LHC

Because the LHC is a proton-proton collider, sizable production of two positively charged W-bosons in association with two jets is possible. This process leads to a distinct signature of same sign high-pt leptons, missing energy and jets. We compute the NLO QCD corrections to the QCD-mediated part of pp -> W+W+jj. These corrections reduce the dependence of the production cross-section on the renormalization and factorization scale to about +- 10 percent. We find that a large number of W+W+jj events contain a relatively hard third jet. The presence of this jet should help to either pick up the W+W+jj signal or to reject it as an unwanted background.Comment: 15 pages, 5 (lovely) figures, v3 accepted for publication in JHEP, corrects tables in appendi

Tensorial Reconstruction at the Integrand Level

We present a new approach to the reduction of one-loop amplitudes obtained by reconstructing the tensorial expression of the scattering amplitudes. The reconstruction is performed at the integrand level by means of a sampling in the integration momentum. There are several interesting applications of this novel method within existing techniques for the reduction of one-loop multi-leg amplitudes: to deal with numerically unstable points, such as in the vicinity of a vanishing Gram determinant; to allow for a sampling of the numerator function based on real values of the integration momentum; to optimize the numerical reduction in the case of long expressions for the numerator functions.Comment: 20 pages, 2 figure

Hypothermia for perinatal asphyxial encephalopathy. A Swiss survey of opinion, practice and cerebral investigations

BACKGROUND: Perinatal asphyxial encephalopathy occurs in 1-per 1000 live births and is associated with high mortality and morbidity. Therapeutic hypothermia increases intact survival and improves neurodevelopmental outcome in survivors.AIMS: To evaluate (i) the opinion and practice of therapeutic hypothermia as a therapy for moderate to severe perinatal asphyxial encephalopathy amongst Swiss neonatologists and paediatric intensive care specialists, (ii) the current clinical management of infants with perinatal asphyxial encephalopathy and (iii) the need for a national perinatal asphyxia and therapeutic hypothermia registry.METHODS: Two web-based questionnaires were sent to 18 senior staff physicians within the Swiss Neonatal Network.RESULTS: Therapeutic hypothermia was considered effective by all responders, however only 11 of 18 units provided therapeutic hypothermia. Cooling was initiated during transfer and performed passively in 82% of centres with a target rectal temperature of 33-34 degrees C. Most units ventilated infants with perinatal asphyxial encephalopathy if clinically indicated and 73% of responders gave analgesia routinely to cooled infants. Neuromonitoring included continuous amplitude integrated EEG (aEEG) and EEG. Neuroimaging included cranial ultrasound (cUS), magnetic resonance imaging (MRI) and computed tomography (CT). Sixty-seven percent of units treating infants with perinatal asphyxial encephalopathy performed MRI routinely. All heads of departments questioned indicated that a "Swiss National Asphyxia and Cooling Registry" is needed.CONCLUSIONS: In Switzerland, access to therapeutic hypothermia is widespread and Swiss neonatologists believe that therapeutic hypothermia for perinatal asphyxia is effective. National cooling protocols are needed for the management of infants with perinatal asphyxial encephalopathy in order to ensure safe cooling, appropriate monitoring, imaging and follow-up assessment. A national registry is needed to collect data on diagnosis, treatment, adverse events and outcome

Snowmass 2001: Jet Energy Flow Project

Conventional cone jet algorithms arose from heuristic considerations of LO hard scattering coupled to independent showering. These algorithms implicitly assume that the final states of individual events can be mapped onto a unique set of jets that are in turn associated with a unique set of underlying hard scattering partons. Thus each final state hadron is assigned to a unique underlying parton. The Jet Energy Flow (JEF) analysis described here does not make such assumptions. The final states of individual events are instead described in terms of flow distributions of hadronic energy. Quantities of physical interest are constructed from the energy flow distribution summed over all events. The resulting analysis is less sensitive to higher order perturbative corrections and the impact of showering and hadronization than the standard cone algorithms

On the Numerical Evaluation of Loop Integrals With Mellin-Barnes Representations

An improved method is presented for the numerical evaluation of multi-loop integrals in dimensional regularization. The technique is based on Mellin-Barnes representations, which have been used earlier to develop algorithms for the extraction of ultraviolet and infrared divergencies. The coefficients of these singularities and the non-singular part can be integrated numerically. However, the numerical integration often does not converge for diagrams with massive propagators and physical branch cuts. In this work, several steps are proposed which substantially improve the behavior of the numerical integrals. The efficacy of the method is demonstrated by calculating several two-loop examples, some of which have not been known before.Comment: 13 pp. LaTe

A Tree-Loop Duality Relation at Two Loops and Beyond

The duality relation between one-loop integrals and phase-space integrals, developed in a previous work, is extended to higher-order loops. The duality relation is realized by a modification of the customary +i0 prescription of the Feynman propagators, which compensates for the absence of the multiple-cut contributions that appear in the Feynman tree theorem. We rederive the duality theorem at one-loop order in a form that is more suitable for its iterative extension to higher-loop orders. We explicitly show its application to two- and three-loop scalar master integrals, and we discuss the structure of the occurring cuts and the ensuing results in detail.Comment: 20 pages. Few typos corrected, some additional comments included, Appendix B and one reference added. Final version as published in JHE

Feynman Rules for the Rational Part of the Standard Model One-loop Amplitudes in the 't Hooft-Veltman γ5\gamma_5 Scheme

We study Feynman rules for the rational part $R$ of the Standard Model amplitudes at one-loop level in the 't Hooft-Veltman $\gamma_5$ scheme. Comparing our results for quantum chromodynamics and electroweak 1-loop amplitudes with that obtained based on the Kreimer-Korner-Schilcher (KKS) $\gamma_5$ scheme, we find the latter result can be recovered when our $\gamma_5$ scheme becomes identical (by setting $g5s=1$ in our expressions) with the KKS scheme. As an independent check, we also calculate Feynman rules obtained in the KKS scheme, finding our results in complete agreement with formulae presented in the literature. Our results, which are studied in two different $\gamma_5$ schemes, may be useful for clarifying the $\gamma_5$ problem in dimensional regularization. They are helpful to eliminate or find ambiguities arising from different dimensional regularization schemes.Comment: Version published in JHEP, presentation improved, 41 pages, 10 figure

Feynman rules for the rational part of the Electroweak 1-loop amplitudes

We present the complete set of Feynman rules producing the rational terms of kind R_2 needed to perform any 1-loop calculation in the Electroweak Standard Model. Our results are given both in the 't Hooft-Veltman and in the Four Dimensional Helicity regularization schemes. We also verified, by using both the 't Hooft-Feynman gauge and the Background Field Method, a huge set of Ward identities -up to 4-points- for the complete rational part of the Electroweak amplitudes. This provides a stringent check of our results and, as a by-product, an explicit test of the gauge invariance of the Four Dimensional Helicity regularization scheme in the complete Standard Model at 1-loop. The formulae presented in this paper provide the last missing piece for completely automatizing, in the framework of the OPP method, the 1-loop calculations in the SU(3) X SU(2) X U(1) Standard Model.Comment: Many thanks to Huasheng Shao for having recomputed, independently of us, all of the ${\rm R_2}$ effective vertices. Thanks to his help and by comparing with an independent computation we performed in a general $R_\xi$ gauge, we could fix, in the present version, the following formulae: the vertex $A l \bar l$ in Eq. (3.6), the vertex $Z \phi^+ \phi^-$ in Eq. (3.8), Eqs (3.16), (3.17) and (3.18

Monodromy--like Relations for Finite Loop Amplitudes

We investigate the existence of relations for finite one-loop amplitudes in Yang-Mills theory. Using a diagrammatic formalism and a remarkable connection between tree and loop level, we deduce sequences of amplitude relations for any number of external legs.Comment: 24 pages, 6 figures, v2 typos corrected, reference adde

A general method for the resummation of event-shape distributions in e⁺ e− annihilation

We present a novel method for resummation of event shapes to next-to-next-to-leading-logarithmic (NNLL) accuracy. We discuss the technique and describe its implementation in a numerical program in the case of e + e − collisions where the resummed prediction is matched to NNLO. We reproduce all the existing predictions and present new results for oblateness and thrust major